Hail Storm is designed to keep your enemies in the cold, while you shatter them into tiny pieces with barrages of ice and frost. The main purpose for this spec is to keep enemies frozen or chilled at all times to allow for better targeting, damage, and survivability.
This Frost spec should have an easier time with adds and group pulls due to the total of 3 Frost Nova types of attacks, being Frost Nova, Ice Ward, and your Elemental’s Freeze spell. With these, it is far easier to single out a large mob from a group, or hitting them all with Blizzard, Cone of Cold, and/or Frozen Orb.
As for the damage aspect, all of these freezing abilities allow for the use of a more powerful version of Ice Lance (4x normal damage) or Deep Freeze (5 sec stun). Also, due to Fingers of Frost (passive) your Frostbolt, Frostfire Bolt, Blizzard, and Frozen Orb all have a chance to make your next Ice Lance or Deep Freeze act as though your enemy was frozen. Invocation will also keep damage up by 25% so long as its used every 40 seconds, easily enough time to dispatch of your foes.
Survivability will be increased not only due to the fact that you are slowing or rooting your enemies, but also due to Ice Barrier and Presence of Mind. The reason why I included Presence of Mind is due to the face that it allows for a split second reaction for a just in case situation. One such situation for me was a point when I had a few adds on me in the Jade Forest, I used Presence of Mind to cast my Frost Bomb on a mob. Yes, it may have only a 1.5 sec cast time, however, when you are near death from having fought several enemies and was interrupted by the current mob from replenishing HP and MP, an instant cast for a few second to an explosion that slows enemies is very handy. Especially when it’s followed by an Ice Barrier then Frost Nova and AoE damage galore!
For Major Glyphs, I chose 2 for damage, and 1 for utility. Cone of Cold and Ice Lance increases the damage of 2 of the main 2 instant cast damage spells that will be used with Frost spec. Frost Nova is a keystone for this spec, so a reduced cool down time is very beneficial. For Minor Glyphs, Momentum is great for gaining more distance from frozen enemies, so long as you make sure there are no enemies in the area you are going. Loose Mana is not a requirement for this spec, but there may be some moments where gaining mana a little slower could be useful, especially since having Invocation, which reduced mana regeneration by 50%.
Try to make sure Ice Barrier stays up at all times along with your Invocation bonus (if you are level 90 that is). Your go to spell will always be Frostbolt. It places up to 3 stacks of vulnerability for a total of 15% to a few of your main spells, and that of your Water Elemental as well. After you have your stacks, or if you feel your enemy is too close, feel free to use Freeze from your Elemental, or go for Frost Nova. I recommend keeping Ice Ward for just in case situations. Then when they are covered in ice, you can go for a Deep Freeze, or If that’s on cool down, go straight for a barrage of Ice Lance and Cone of Cold. Also, be sure to use Ice Lance whenever you have a proc from your Fingers of Frost (or Deep Freeze if necessary). As for groups, be sure to put in a Frost Bomb as early as possible. Then try to get the group of enemies clustered together, so you can freeze them with one of your 3 options from above, then Blink and us Frozen Orb and Blizzard.